Integrated optical circuits are needed in communications engineering for various purposes, such as for the distribution, combining, spectral partitioning or switching of information-modulated light fluxes. In addition, it is also possible to implement other circuits with the aid of optical structures, such as computer circuits.
At present, integrated optical circuits are constructed using waveguides made of polymers or III-V compound semiconductors which are structured by lithographic processes.
Suitable as the optically active elements of such circuits are, inter alia, photonic crystals which, because of their small geometrical dimensions, require a waveguide pattern into which they are inserted in order to develop their full effect. Such waveguide patterns are usually strip waveguides made of polymer or semiconductor material.
These waveguide patterns can be produced in a complementary structure which, through its form, prevents the propagation of the photon pulses in the matter and, through selective built-in defects, allows propagation into otherwise completely reflecting matter. In this context, there is not a step change (sudden change) in refractive index as in the guiding of waves in optical waveguides formed by doping or in the form of strip waveguides, instead--theoretically stated--forbidden bands limit the state solution of the eigensolutions desired for specific wavelengths for propagating these waves. These waveguides are described, for example, in a reference by A. Mekis et AL in Physical Review Letters, Volume 77, No. 18, p. 3787.